Electrical heaters



15, 1964 H; F. DICKSON, JR., ETAL 3,160,946

ELECTRICAL HEATERS Filed March 11, 1960 3 Sheets-Sheet l 1954 H; F. DICKSON, JR, ETAL 3,160,946

ELECTRICAL HEATERS Filed March 11, 1960 3 Sheets-Sheet 2 INVENTORS He/berf E D/c/rsm Jr: BY Paul Haas MZM ATTORNEY Dec. 15, 1 H.- F. DICKSON, JR., ETAL 3,160,946

ELECTRICAL HEATERS Filed March 11, 1960 3 Sheets-Sheet 3 INVENTORS l-lerberf D/cksan Jfi Pau/ Haas W W ATTJRNEY United States Patent 3,169,946 ELECTRICAL WATERS Herbert F. Dickson, in, and Paul Haas, Seneca Falls, N.Y., assignors t0 Sylvania Electric Products Inn, a

corporation of Delaware Filed Mar. 11, 196i), Ser. No. 14,471 2 Claims. (U. 29-15562) This invention relates to heaters for electrical devices and more particularly to heaters adapted for use with thermionic cathodes of the type employed in electron tubes.

It has been proposed that a low heater power type of cathode assembly may be used in electron tubes. One form of such a heater-cathode assembly employs an insulated heater Wire embedded in the cathode base. In this structure, the cathode base metal material in powdered form is deposited about the heater wire and subsequently the powder is pressed into a pellet and sintered.

It is difficult to make a satisfactory heater embedded cathode assembly. The pellet itself is small and the requirements for electron emission at low heater power are such that a considerable length of the heater wire must be packed within the pellet. In order to achieve the proper uniform temperature of the cathode pellet, the heater should physically be uniformly and symmetrically placed, there should be no shorted sections of the heater, and the heater-cathode leakage should be a minimum.

The fabrication of the heater itself is an important factor in. achieveing the requirements enumerated above. For inst-ance, the heater wire should be formed in to a configuration to provide a relatively large amount of wire within the pellet, and the configuration should be symmetrical with uniform sectional spacings. In addition, the insulating coating should be of uniform thickness over the entire embedded heater portion; 7

Accordingly, it is an object of this invention to fabricate a heater adapted for use in heater embedded cathode assemblies.

It is a further object to form a substantially flat heater coil with uniform coil wraps, uniform spiral turn spacings and a uniform coating. V

The foregoing objects are achieved in one aspect of the invention by the provision of a process and apparatus for forming a-spiral reverse coil wound heater. The resistance heater wire is spiral wound up on a mandrel and this wire spiral and mandrel assembly are subsequently twisted into a reverse wound flat coil with substantially uniformly spaced wraps. The mandrel is then removed and the heater Wire spiral is coated withinsulating material. In the coil winding operation, the mandrel is placed in a chuck and twisted with the ends of the mandrel arrested from rotational movement by stop pins.

For-a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a length of heater wire spiral wound upon a mandrel;

FIG. 2 shows the heater coil winding device;

FIG. 3 is an enlarged top view of the heater winding chuck employed with the device of FIG. 2;

FIG. 4 illustrates a cross sectional view of the heater winding device;

FIGS. 5, 6 and 7 illustrate the manner of forming the reverse heater coil;

FIG. 8 illustrates the method of annealing the formed heater coil;

FIG. 9 shows the manner of removing the mandrel from the heater spiral;

' FIG. 10 illustrates the heater coating operation; and

FIG. 11 is a plan view of a finished spiral reverse coil wound flat heater.

2 3,160,946 C Patented Dec. 15, 1964 Referring to the drawings, a spiral reverse wound substantially flat coiled heater 13 is shown in FIG. 11. The heater resistance wire 15 is formed into a spiral which is in turn twisted as a reverse wound coil. Each turn of the spiral is coated with an electrical insulating material 17 except the last several turns. The straight wire ends 19 are left uncoated to allow for welding to the heater power supply leadswhen employed in an electron tube.

Heater 13 is uniquely adapted to provide maximum heat for a given area with minimum power. Due to its relatively small size, compactness and uniform spacing and symmetry, the heater is suitable for use in an indirectly heated cathode assembly wherein the heater is embedded in the cathode base material.

FIG. 1 illustrates a spiral length of heater wire 15 which has been selected to provide the heat necessary for a given application at a given power rating. The wire, wire may be tungsten, is Wound up a mandrel 21 made of, for instance, molybdenum. The diameter of the wire, turns per inch of the spiral, and length ofthe heater can be varied in order to produce the desired electrical characteristics. In the spiral winding operation, the wire 15 is preferably stretched beyond the elastic limit so. that the initial spiral shape will be substantially maintained after mandrel 21 has been removed as will be hereafter described.

The mandrel and wire spiral assembly 22 are subsequently formed or twisted into a substantially flat reverse wound coil. A winding device 23 is provided for the purpose of accomplishing thisreverse winding operation. Referring to FIGS. 2' through 7, device 23 comprises a cylindrical block 25 having an aperture 27 extending longitudinally therethrough; The upper heater supporting surface 29 may be tapered. a slight amount, e.g., several degrees, radically symmetrically downward from aperture 27 to prevent the Wire spiral from climbing over itself during the twisting operation.

Mounted upon surface 29 are two frusto-conical shaped,

arresting pins 31. The small diameters of the pins lie adjacent surface 29 so that the pins are beveled outwardly to prevent the ends of mandrel 21 from riding upwardly and to provide a drag on the mandrel during the coil wrapping operation. Pins 31 preferably exceed the height of the spiral of wire and are oppositely disposed from and equally radially spaced'from the center of aperture 27. For simple reverse wound coils, the pins maybe permanently located as shown. However, for larger or more intricate coil configurations, it may be desirable to either move the pins radially during the winding operation surface 29.

Block 25 rests upon a cylindrical base 33 having a rod.

35 passing through aperture 27. The upper end of the rod has a chuck 36 formed with a spiral and mandrel assembly receiving slot 37 defined by laterally spaced slot walls 39. The opposed outside edges 41 of the walls are recessedfrom the rod periphery and are curved to provide the initial coil wrap configuration. The height of the walls preferably exceed the diameter of the wire spiral. Since block 25 merely rests upon base 33, these parts may be rotated relative to one another. The amount of rotation of, for instance, base 33 or chuck 36 relative to block 25 may be ascertained from pointer 43 and markings 45. Also, base 33 and block 25 may reciprocate longitudinally relative to one another so that chuck 36 can be retracted to a mandrel assembly release position.

In the reverse coil winding operation, assembly 22 is first placed within slot 37 as shown in FIG. 2. When a symmetrical reverse coil such as is illustrated in FIGS. 7 and 11 is desired, the center of assembly 22 is positioned at the center of the slot. The initial partial Wrap of the coil is achieved by applying tension to the mandrel and rotating base 33 toprovide rotation of chuck 36, FIG. 5. The tension may be'applied by holding the ends of mandrel 21 to provide drag and therefor bending around the edges 41 of Walls 39, or it may be accomplished by pressing downwardly against the spiral and mandrel toachieve the same results. After the partial first wrapis made, chuck '36 isfurther rotated until assembly 22 contacts arresting pins 31. Continued rotation of the chuck wraps the spiral wire and mandrel assembly as shown in FIG. 6. 'Due to the beveled sides of arresting pins 31, assembly 22 tends to become trapped between the pins and the upper block surface 29. This trapping action creates a drag onthe mandrel and'thereby provides relatively tight wrapping. During this latter rotational movement," some overwrapping is desired. The amount of overwrapping' depends upon the spacing required between sections of the coil 13.

. After the spiral wire and mandrel assembly 22 have been wound as a'reverse coil as shown in FIG. 6, chuck 36 is then rotated in the opposite direction. During this rotation, assembly'22 contacts pins 31 on the opposite sides thereof, which causes the coil to unwrap an amount sufiicient to provide the coil spacing desired, see FIG. 7. The ends of the coil therebyextend tangentially from the curvature of the outside turns. Rod'35 with its chuck 36 is then retracted into aperture 27 to release the substantially'flat reverse coil formed from assembly 22. The releasing. operation is achieved bymoving base 33 or block 25 longitudinally away from one another.

After assembly 22 has been wound into a reverse coil, it is placed in an oven (not shown) and-fired between flat tungsten plates 47, see FIG. 8. The firing operation may be performed in a wet hydrogen reducing atmosphere in accordance-with the temperature-time relationship reremoves the mandrel by selective etching, see FIG. '9.

A suitable solution such as one consisting of 50 percent nitric acid, 30 percent sulfuric acid and 20'percent water;

by weight, is capable of etching a .002 inch diameter molybdenumman'drel'in a relatively short time attackingthe tungsten wire 15. r

The reverse wound coil of wire may be subsequently rinsed in deionized water and subsequently electrophoretically coatedin tank 50 with the insulating material 17. During the coating'operatiomthe coil of wire 15 is held in electrode 51, FIG. 10, so that the area'tobe coated is exposed to coating bath 53, which may consist of a dispersion. of aluminumoxide'in a partiallyrhyd'rolized aluminum nitrate and alcohol solution. shields the last several turns of wire 15 and the ends 19 so that no coating is deposited thereon.v The uncoated portions of the wire are utilized for a welding connection during ultimate assembly in an electron'tube. ,An anode 55 is also disposed in bath 53, and positive and negative potentials are applied to anode 55 and electrode 51 respec-. tively to electrophoretically ooatwire 15 in a manner well understood in the art. spacing between the spiral turns and coil wraps, the insulating coating is uniformly deposited overv the desired area.

without Electrode 51 After coating, Wire is subsequently fired between flat plates of the type shown in FIG. 8. Here again, a'wet hydrogen atmosphere may be used during this operation. Firing of the wire assures flatness of the coil, it removes any distortion in the reverse coil wraps, and it sinters the insulating coating 17 to produce the, reverse coil wound spiral heater 13, shown in FIG. 11.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications 7 may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

l. A process for forminga spiral reverse coil wound flatheater adapted'for use in anelectro-n' discharge device comprising the steps of winding a spiral of heater'wire upon amandrel, holding the mandrel at a position along an axis intermediate the ends thereof, forming a substantially fiat reverse wound mandrelcoil byrotating said mandrel in a plane about said axis withthe ends thereof rotatively arrested-and-guided for frictionally inhibited movement'substantially'in said plane'toward the mandrel coil during rotation, heating the coiledmandrel arid supportedwire spiral in a reducing atmosphere between flat plates'to anneal the coiled spiral, removing the mandrel from the reverse coiled spiral of wireby selectively etching away'the mandrel, and electrophoretically coating the wire with an 7 electrical insulating material.

2. A'process for forming a-s pir'al reverse coil wound flat-heater adapted for use inan electron discharge device comprising the steps of winding heater wire upon a deformablemandrel under tension to provide a permanently elongated spiral of wire upon the mandrel; holding the mandrel at a position along an a-Xisintermediatethe ends plane about said axis-with the." ends thereof rotatively arrested and giidedforfr'ictionally inhibited movement substantially in said plane toward the mandrel coil during rotation to' provide substantially tight wrapping of said Dueto the uniformity of tially'uniformlyspaced wraps; heating the coiled mandrel and supported wire spiral in areducing atmosphere between flat pl'at'es'to anneal the coiled'spiral; removing the *ma-ndr'el from the reverse coiled spiral of wire by selectively etching away the -mandrel;,-and coating the wire with an electrically insulatingmaterial.

References Cited in the file of this patent UNITED STATES PATENTS Adair -t. May 17, 1960 

1. A PROCESS FOR FORMING A SPIRAL REVERSE COIL WOUND FLAT HEATER ADAPTED FOR USE IN AN ELECTRON DISCHARGE DEVICE COMPRISING THE STEPS OF WINDING A SPIRAL OF HEATER WIRE UPON A MANDREL, HOLDING THE MANDREL AT A POSITION ALONG AN AXIS INTERMEDIATE THE ENDS THEREOF, FORMING A SUBSTANTIALLY FLAT REVERSE WOUND MANDREL COIL BY ROTATING SAID MANDREL IN A PLANE ABOUT SAID AXIS WITH THE ENDS THEREOF ROTATIVELY ARRESTED AND GUIDED FOR FRICTIONALLY INHIBITED MOVEMENT SUBSTANTIALLY IN SAID PLANE TOWARD THE MANDREL COIL DURING ROTATION, HEATING THE COILED MANDREL AND SUPPORTED WIRE SPIRAL IN A REDUCING ATMOSPHERE BETWEEN FLAT PLATES TO ANNEAL THE COILED SPIRAL, REMOVING THE MANDREL FROM THE REVERSE COILED SPIRAL OF WIRE BY SELECTIVELY ETCHING AWAY THE MANDREL, AND ELECTROPHORETICALLY COATING THE WIRE WITH AN ELECTRICAL INSULATING MATERIAL. 